Abstract: The granite weathering crust exhibits a typical dual structure,consisting of an upper loose residual soil layer and a lower dense weathered rock layer. This distinctive stratigraphic configuration leads to complex failure mechanisms in granite slopes during rainfall events. This study investigated the mass landslide event that occurred on June 12,2019, in Mibei Village,Longchuan County,Guangdong Province. A typical granite weathering crust profile was obtained through field surveys,and a slope geological model was established based on similarity criteria to examine the rainfall infiltration processes and failure mechanisms of slopes with varying residual layer thicknesses under heavy rainfall conditions. The results revealed distinct infiltration behaviors and failure mechanisms depending on the residual layer thickness: (1)For a 10 cm residual layer,rainfall rapidly infiltrated to the soil-rock interface. Due to the higher permeability of the upper soil compared to the lower rock layer,water accumulated at the interface,causing rapid saturation of the residual soil. This led to integrated flow-slide failure without a clearly defined slip surface.(2)With a 20 cm residual layer,longer infiltration time was required to reach the interface. Water accumulation at the interface significantly reduced the shear strength of the adjacent residual soil,resulting in retrogressive sliding along the interface initiated by seepage traction at the slope toe.(3)For a 30 cm residual layer,rainfall did not penetrate to the soil-rock interface. Failure occurred as a thrust-type landslide within the residual layer,driven by hydrostatic pressure along the base of the saturated zone.